Cancer in the colon and cancer in the rectum, often referred to together as colorectal cancer, is the third most common cancer diagnosed in both men and women in the U.S. excluding skin cancers, according to the American Cancer Society.

Among the risk factors that can increase your risk of colorectal cancer are certain genetic syndromes, including familial adenomatous polyposis. This is a rare condition caused by a defect in the adenomatous polyposis coli gene. Most people inherit the gene from a parent, but for 25% to 30% of people, the genetic mutation occurs spontaneously.

With this condition, extra tissue, called polyps, forms in your colon and rectum. Polyps also can occur in the upper gastrointestinal tract, especially the upper part of your small intestine. If untreated, the polyps in the colon and rectum are likely to become cancerous when you are in your 40s.

Most people with familial adenomatous polyposis eventually need surgery to remove the large intestine to prevent cancer. The polyps in the upper part of the small intestine also can develop cancer, but they usually can be managed by careful monitoring and regularly removing the polyps.

Some people have a milder form of the condition, called attenuated familial adenomatous polyposis. People with this milder form usually have fewer colon polyps and develop cancer later in life.

Symptoms

The main sign of familial adenomatous polyposis is hundreds or even thousands of polyps growing in your colon and rectum, usually starting by your mid-teens. The polyps are nearly 100% certain to develop into colon cancer or rectal cancer by the time you're in your 40s.

Risk factors

Familial adenomatous polyposis is caused by a defect in a gene that's usually inherited from a parent. But some people develop the abnormal gene that causes the condition. Your risk is higher if you have a parent, child, brother or sister with the condition.

Prevention

Preventing familial adenomatous polyposis is not possible, since it is predominantly an inherited genetic condition. However, if you or your child are at risk because of a family member with the condition, you will need genetic testing and counseling.

A blood test can determine if you carry the abnormal gene that causes familial adenomatous polyposis. Ruling it out spares at-risk children years of screening and emotional distress. For children who carry the gene, appropriate screening and treatment greatly reduces the risk of cancer.

For people at risk, it's important to be screened frequently, starting in childhood. Annual exams can detect the growth of polyps before they become cancerous.

If you have been diagnosed with familial adenomatous polyposis, you will need regular screening, followed by surgery if needed. Surgery can help prevent the development of colorectal cancer or other complications.

Treatment

Treatment for familial adenomatous polyposis begins with your health care professional removing any small polyps found during your colonoscopy exam. Eventually, though, the polyps will become too numerous to remove individually, usually by your late teens or early 20s. Then you will need surgery to prevent cancer developing. You also will need surgery if a polyp is cancerous. If you have attenuated familial adenomatous polyposis — the milder form of the condition, you may not need surgery.

Surgery doesn't cure familial adenomatous polyposis. Polyps can continue to form in the remaining or reconstructed parts of your colon, stomach and small intestine. Depending on the number and size of the polyps, having them removed endoscopically may not be enough to reduce your risk of cancer. You may need additional surgery. You also will need regular screening — and treatment if needed — for the complications of familial adenomatous polyposis that can develop after colorectal surgery.

Connect with others talking about familial adenomatous polyposis and colorectal cancer in the Colorectal Cancer support group on Mayo Clinic Connect, an online patient community moderated by Mayo Clinic.

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